<?php
$str = "fmsofdsf";
var_dump(strpos($str,"a"));//查找字符串，返回下标位置
echo "<br>";
//---------------------------------字符串替换---------------------------------------//
$str_res = str_replace("f","a",$str);
echo $str_res;
echo "<br>";
//---------------------------------重复执行---------------------------------------//
echo  str_repeat("我爱fr！","99");
echo "<br>";
//---------------------------------大写转小写---------------------------------------//
var_dump(strtolower($str));
echo "<br>";
var_dump(strtoupper($str));
echo "<br>";
//---------------------------------时间---------------------------------------//
echo time();
echo "<br>";
echo date("Y-m-d H:i:s");
echo "<br>";
echo strtotime("2019-12-05 16:22:36");